Publication date: Available online 4 March 2017Source:The Spine JournalAuthor(s): Matt Fernandez, Lucia Colodro-Conde, Jan Hartvigsen, Manuela L. Ferreira, Kathryn M. Refshauge, Marina B. Pinheiro, Juan R. Ordoñana, Paulo H. FerreiraBackground context Pain is commonly associated with symptoms of depression or anxiety, although this relationship is considered bi-directional. There is limited knowledge regarding causal relationships. Purpose To investigate whether chronic low back pain (LBP) increases the risk of depression or anxiety symptoms, after adjusting for shared familial factors. Study Design A longitudinal, genetically informative study design from the Murcia Twin Registry in Spain. Patient Sample Patient sample included 1269 adult twins with a mean age of 53 years. Outcome MeasuresThe outcome of depression or anxiety symptoms was evaluated with EuroQol (EQ-5D) questionnaire. Methods Using logistic regression analyses, twins were initially assessed as individuals in the total sample analysis, followed by a co-twin case-control, which partially [dizygotic twins (DZ)] and fully [monozygotic twins (MZ)] adjusts for shared familial factors. There was no external funding for this study and no conflict of interest is declared. Results There was a significant association between chronic LBP and the risk of depression or anxiety symptoms in the unadjusted total sample analysis – odds ratio (OR): 1.81 (95% Confidence Interval [CI]: 1.34 – 2.44). After adjusting for confounders, the association remained significant (OR: 1.43 (95% CI: 1.05 – 1.95), although adjusted co-twin case-control were non-significant in DZ (OR: 1.03, 95% CI: 0.50-2.13) and MZ twins (OR: 1.86, 95% CI: 0.63-5.51). Conclusion The relationship between chronic LBP and the future development of depression or anxiety symptoms is not causal. The relationship is likely to be explained by confounding from shared familial factors, given the non-statistically significant associations in the co-twin case-control analyses.